Briefly, a tubular skylight such as those mentioned in U.S. Pat. Nos. 5,896,713 and 6,035,593, both of which are owned by the same assignee as is the present invention and both of which are incorporated herein by reference, includes a tube assembly mounted between the roof and ceiling of a building. The top end of the tube assembly is covered by a roof-mounted cover, while the bottom end of the tube assembly is covered by a ceiling-mounted diffuser plate. With this combination, natural light external to the building is directed through the tube assembly into the interior of the building to illuminate the interior.
As understood herein, the tube with vertical sides reflects light in the same angle each reflection, which angle depends on the sun's elevation in the sky and thus varying throughout the day, limiting the efficiency and effectiveness of the diffuser in controlling the distribution of light in the building.